Can you sit if you have fat transfer to hips and top of butt only? If not, how long to stay off?

Always ask your surgeon as this will depend upon surgeon preference and the specifics of your surgery.
In addition, I tell my BBL patients to minimize sitting.  If they have to sit, it is critical that every 30 minutes or an hour that patients get up and stand for a few seconds to take the pressure off.   This reduces the chance for fat necrosis.  After 6 weeks the fat has revascularized, and you have a very good idea of your final results.  

Dear aokayyy,
I instruct my patients not to sit for 2 solid weeks. We provide them a specialized pillow that our patients can sit on during that time. They can sleep on their stomachs or sides. Fat viability depends a lot of surgeon technique. The fat has to be placed back into the buttocks as soon as possible so that it has a greater chance of survival. It has to be placed carefully so that not too much fat is placed in only one area
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery